Evaluation of two different scrap tires as hydrocarbon source by pyrolysis

Suat Ucara, Selhan Karagoza, Ahmet R. Ozkanb, Jale Yanikc,*

aChemistry Program, IMYO, Dokuz Eylul University, Buca, Izmir 35160, TurkeybPetkim Holding Co, Quality Control and Technical Service, Aliaga, Izmir, Turkey

cEge University, Faculty of Science, Department of Chemistry, Bornova, Izmir 35100, Turkey

Received 25 October 2004; received in revised form 24 March 2005; accepted 5 April 2005

Available online 12 May 2005

Abstract

The main objective of the present study is to investigate the effect of the polymer types in scrap tires on the pyrolysis products. Two

different types of scrap tires (passenger car tire, PCT and truck tire, TT) have been pyrolyzed in a fixed bed reactor at the temperatures of 550,

650 and 800 8C under N2 atmosphere. Pyrolysis products (gas, oil and carbon black) obtained from PCT and TT were investigated

comparatively. The gaseous products were analyzed by GC–TCD. The psychical and chemical properties of pyrolytic oils were characterized

by means of GC–FID, GC–MS, 1H NMR. In addition, boiling point distributions of hydrocarbons in pyrolytic oils were determined by using

simulated distillation curves in comparison with commercial diesel fuel. The production of activated carbon from pyrolytic carbon blacks

(CBp) was also carried out. The composition of gaseous products from pyrolysis of PCT and TT were similar and they contained mainly

hydrocarbons (C1–C4). Pyrolytic oils were found lighter than diesel but heavier than naphtha. The physical properties of pyrolytic oils from

PCT and TT were similar at the same temperature. However, the composition of aromatic and sulphur content from pyrolysis of PCT was

higher than that of TT. Furthermore, TT derived pyrolytic carbon black was found more suitable for the production of activated carbon due to

its low ash content.

q 2005 Elsevier Ltd. All rights reserved.

Keywords: Scrap tires; Pyrolysis; Activated carbon

1. Introduction

How to deal with the waste materials such as scrap tires is

a big economic and environmental concern. Scrap tires are

generally dumped in massive stockpiles, which provide

ideal breeding grounds for disease carrying mosquitoes and

other vermin. Dumping of the scrap tires may also cause a

fire hazard. Moreover, there are different alternatives have

been using for tire recycling such as retreating, reclaiming,

incineration, grinding etc. However, all of them have

significant drawbacks and/or limitations [1]. Pyrolysis can

be considered as a viable recycling technology to treat the

scrap tires. It has a number of advantages as a treatment

option since the derived oils can be used as fuels or added to

petroleum refinery feed stocks, they also be an important

0016-2361/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.fuel.2005.04.002

* Corresponding author. Tel.: C90 232 3884000x2386; fax: C90 232

3888264.

E-mail address: jyanik@sci.ege.edu.tr (J. Yanik).

source for refined chemicals. The pyrolysis gas can be used

as fuel in the pyrolysis process. The solid residue has a good

candidate for the solid fuel or for the low grade carbon

black.

There have been many reports on the pyrolysis of scrap

tires [1–5]. Rodriguez et al. [1] explored the pyrolysis of

scrap tires under the nitrogen atmosphere at 300, 400, 500,

600, and 700 8C. They reported that there is no significant

influence of temperature on the amount and characteristics

of pyrolysis products over 500 8C. Pyrolysis gases were

composed of hydrocarbons of which C1 and C4 are

predominant together with some CO, CO2 and H2S. It was

also reported that tire pyrolysis liquids were complex

mixture of C5–C20 organic compounds. Roy et al. [4] have

investigated the vacuum pyrolysis of scrap tires at a

temperature of 480–520 8C and a total pressure lower than

10 kPa. They concluded that the pyrolytic gas can be used as

a make up heat source for the pyrolysis process and the total

pyrolytic oil can be used as a liquid fuel. Temperature

selective condensation of scrap tire pyrolytic oils to

maximize the recovery of single aromatic compounds was

also studied [5]. The distribution of oil in the condenser

Fuel 84 (2005) 1884–1892

www.fuelfirst.com

Table 2

Proximate and ultimate analyses of scrap tires

Type of scrap tire Passenger car tire (PCT) Truck tire (TT)

Proximate analysis (as received, wt%)

Moisture 1.6 1.4

Volatile matter 58.2 66.1

Fixed carbon 21.3 27.5

Ash 18.9 5.0

Ultimate analysis (dry, %)

C 74.30 83.20

H 7.20 7.70

N 0.90 1.50

Oa 15.89 6.16

S 1.71 1.44

GCVb, MJ kgK1 30.5 33.4

a Calculated from difference.b Gross calorific value.

S. Ucar et al. / Fuel 84 (2005) 1884–1892 1885

system was found to be optimal in terms of the amount of oil

condensed, the range of molecular weights of the oil and the

concentrations of toluene, xylene and limonene when pall

rings were used as the condenser packing material.

In many scientific laboratory tyre-pyrolysis studies

reported in the literature, the effect of processes parameters

such as, temperature, heating rate, pressure, type of reactor

on the product distribution from pyrolysis and product

composition was investigated. In the present study, two

different types of scrap tire have been pyrolyzed at the

temperatures of 550, 650 and 800 8C under N2 atmosphere.

The effect of the polymer types in scrap tires on the yields

and compositions of pyrolysis products were investigated.

The compositions of gaseous products was determined for

the representative temperature (650 8C). The physical and

chemical properties of pyrolytic oils were determined by

using various techniques i.e. 1H NMR, GC–MS and

elemental analysis. In addition, the pyrolytic carbon black

from the pyrolysis of scrap truck tires was also utilized to

produce activated carbon.

2. Materials and methods

2.1. Materials

Passenger Car Tire (PCT) and Truck Tire (TT) were

supplied by Akin Rubber Plant-Samsun, Turkey (a rubber

recycling enterprise). Scrap tire samples were shredded,

crumbed and sieved from the sidewall rubber of scrap tires

to produce a size of 1.5–2.0 mm. The scrap tires contained

no steel thread and the textile netting. The polymer types in

rubber content of scrap tires (Table 1) were determined in

Brisa Co, Izmit, Turkey by serial Curie point pyrolysis-gas

chromatography (Py-GC) according to ASTM D3452-93.

Proximate and ultimate analyses of the scrap tires are shown

in Table 2.

2.2. Pyrolysis process

Pyrolysis experiments were carried out under nitrogen

atmosphere at the temperatures of 550, 650 and 800 8C. The

pyrolysis experiments were performed in a fixed bed design

and stainless steel reactor (L; 210 mm; Ø; 60 mm) under

atmospheric pressure using a semi-batch operation. A

schematic experimental set-up is shown in Fig. 1. The

reactor was purged before experiments by nitrogen gas flow

of 25 ml/min for 10 min to remove air inside. In a typical

Table 1

Rubber composition of scrap tires, wt%

PCT TT

Natural rubber (NR) 35 51

Styrene butadiene rubber (SBR) – 39

Butadiene rubber (BR) 65 10

pyrolysis experiment, a quantity of 130 (G0.5) g of scrap

tire was loaded and then the reactor temperature was

increased by a heating rate of 7 8C/min up to the desired

pyrolysis temperature and hold for 1 h at the desired

temperature. The nitrogen gas swept the volatile products

from the reactor into the collection traps. Liquid products

were condensed in the first two traps by cooling with ice

bath. Non-condensable volatiles were passed through the

last two traps containing lead nitrate solution (33 wt%) to

absorb the H2S and then the remaining gases were collected

in Tedlar plastic bags. The liquid product contained the

aqueous and organic phase. Organic phase (pyrolytic oil)

was separated from aqueous phase by centrifugation. The

pyrolysis of the experiments was repeated three times. The

pyrolysis yields presented are the mean value of three

equivalent experiments and the standard deviation of the

data is also presented at Table 3.

2.3. Gas analyses

In some of the experiments, the pyrolysis gases were

totally collected in Tedlar bag and analyzed by gas

chromatography, HP model 5890 series II with a thermal

conductivity detector. A stainless steel packed column

(6.0 m!1/8 in. Propack Q, 2.0 m!1/8 in. 5A molecular

sieve, serially connected to each other) was used. The

separation of CO2, C1, C2, C3, C4, C5 and C6 hydrocarbons

was done with Propack Q column and the separation of O2,

N2 and CO was carried out with MS 5A column.

The amount of hydrogen sulphur in the gaseous products

was determined as lead sulphur precipitate, which was

formed from the reaction between H2S and lead nitrate in

traps. The lead sulphur precipitate were filtered, washed

with distillated water, dried at 110 8C and weighted.

2.4. Oil analyses

Pyrolytic oils obtained under the same condition were

well mixed and homogenized prior to analysis being made.

Fig. 1. Experimental set-up.

Table 3

Product distributions from pyrolysis of scrap tires, (mean valueGstandard

deviation)

Feed Passenger car tire (PCT)

S. Ucar et al. / Fuel 84 (2005) 1884–18921886

Some physical properties of pyrolytic oils were determined

by using the following standard methods; ASTM D1298,

ASTM D445, ASTM D93 and ASTM D240. Elemental

analysis (C, H, and N) of oils was determined with an

elemental analyzer (Carlo Erba 1106). Sulphur amount in

pyrolytic oils were determined by using Ultraviolet

Fluorescence according to ASTM D5453. The pyrolytic

oils were analyzed by gas chromatography with a flame

ionization detector using a Hewlett–Packard Model

6890GC. The column was HP z-530, 300 column (30 m

long!0.32 mm diameter) coated with phenylmethylsilox-

ane cross linked at a thickness of 0.50 mm. GC-FID was

programmed from 40 to 280 8C at 5 8C/min with a final

holding time of 30 min. The data obtained from GC-FID

was used to evaluate the simulated distillation curves [6].

Identification of compounds in pyrolytic oils was carried out

by gas chromatograph equipped with a mass selective

detector. (Column, HP-1; cross-linked methyl siloxane,

25!0.32 mm!0.17 mm; temperature program, 40 8C (hold

10 min)/300 8C (rate 5 8C/min) hold for 10 min). Com-

pounds were identified by means of the Wiley library-HP

G1035A and NIST library of mass spectra and subsets HP

G1033A. 1H NMR analyses of pyrolytic oils were recorded

with a Varian AS-400 using CDCl3 as solvent.

Temperature, 8C 550 650 800

Reaction products, wt%

Gasa 7.4G2.5 7.6G2.7 7.8G2.3

Oil 47.4G1.8 48.4G2.4 47.2G1.9

Water 3.2G0.9 2.3G0.5 3.5G0.4

Carbon black 42.0G2.5 41.7G2.7 41.5G2.3

Feed Truck tire (TT)

Temperature, 8C 550 650 800

Reaction products, wt%

Gasa 7.6G2.8 7.6G2.4 8.8G2.7

Oil 55.6G1.3 56.0G1.8 55.1G2.0

Water 3.0G0.5 2.6G1.1 2.9G0.9

Carbon black 33.8G2.8 33.8G2.4 33.2G2.7

a Calculated from mass balance.

2.5. Demineralization and activation of pyrolytic

carbon black

The pyrolytic carbon black (CBp) obtained from the

pyrolysis of scrap truck tires at 800 8C was demineralized to

decrease its inorganic content. CBp was treated with HCl

solution (10 wt%) at 100 8C for 2 h. After HCl treatment,

the CBp were washed with distillated water until no chlorine

ions could be detected and then was dried at 100 8C for 24 h.

Activation process was carried out in the pyrolysis

reactor by carbon dioxide. In activation process, non-

demineralized and demineralized pyrolytic carbon black

was heated up to 900 8C under a flowing (25 ml/min)

nitrogen atmosphere. When 900 8C was reached, the inert

atmosphere was rapidly substituted by flowing (350 ml/min)

carbon dioxide. The tested activation times were 2, 4, 6 and

8 h. At the end of desired the activation time, reactor was

cooled to room temperature under nitrogen atmosphere. The

resulting carbons (activated carbon) from activation process

were weighted to calculate the burn off value and were

ground and sieved to a particle size !100 mm for the

amount of nitrogen adsorption (BET analysis).

3. Results and discussion

3.1. Pyrolysis of scrap tires

The product distributions from pyrolysis of PCT and TT

at different temperatures are presented in Table 3. It can be

seen that product distributions of PCT and TT did not

Table 4

Composition of the gaseous products from pyrolysis of scrap tires at 650 8C

Feed PCT TT

Gases, mol%

C1 23.92G0.36 24.21G0.34

C2 9.00G0.14 8.12G0.12

C2a 4.37G0.07 4.43G0.09

C3 11.80G0.18 12.56G0.19

C4 7.64G0.11 9.53G0.14

C5 10.74G0.16 12.20G0.18

C6 0.19G0.01 0.22G0.03

CO 1.15G0.0.21 2.02G0.03

CO2 2.41G0.16 6.08G0.09

O2 2.72G0.04 1.54G0.02

H2 26.06G0.39 19.09G0.29

S. Ucar et al. / Fuel 84 (2005) 1884–1892 1887

change significantly with increasing the temperature.

The thermochemical conversion of rubber from scrap tires

by pyrolysis and hydropyrolysis has been studied by Mastral

et al. [2]. They observed that neither the total conversion nor

liquid yield increased with increasing temperature above

500 8C for the pyrolysis at a heating rate of 300 8C minK1.

Similar results have been reported by other researchers. The

pyrolysis of scrap tires was carried out in a fixed bed reactor

at the temperatures from 300 to 700 8C at the heating rate of

15 8C minK1 [1,7,8]. It was reported that there is no influence

of the temperature on the product distributions over 500 8C.

On the contrary, the decrease in liquid yields with increasing

temperature and the corresponding increase in gas yield,

have been observed by other workers. Day et al. [9] have

carried out the pyrolysis of auto shredder residue in a

laboratory screw kiln reactor from 500 to 700 8C. They found

that the yield of oil fraction was high at the lower pyrolysis

temperatures. In another study, pyrolysis of scrap tires in

circulating fluidized bed reactor from 360 to 810 8C was

carried out. The yield of oil increased first to a maximum

value of about 50% at 450 8C, and then decreased with the

increase of the temperature [10]. Similarly, Gonzalez found

an increase in gas yield and a decrease in oil yield as the

temperature was raised from 575 to 700 8C [11]. On the other

hand, William studied pyrolysis from 300 to 720 8C and

observed that char yield decrease while liquid and gas yield

increased until 600 8C after which there was a minimal

change to product yield [12]. It is, therefore, obvious that not

only the influence of temperature, but also the pyrolysis

yields will vary from some studies to the others. It can be

concluded that product distribution from pyrolysis of scrap

tires depends on the process parameters values i.e. tempera-

ture, heating rate, pressure, residence time, type of reactor. In

the present study, the product distributions from the pyrolysis

of TT and PCT were quite different from each other. For all

temperatures, in the case of TT, the oil yield was higher and

the yield of pyrolytic carbon black was less than that of PCT

because of the differences in rubber composition of raw scrap

tires (Table 1). In addition, the ash amount of tyres had also

effect on the pyrolysis yield.

3.2. Composition of gaseous products

The gas composition is presented in Table 4 for the

representative pyrolysis temperature (650 8C). It can be seen

that gaseous products are mainly composed of hydrogen

with hydrocarbons (C1–C6). Other gases present were CO,

CO2, O2. Moreover, the total amount of H2S was

determined. The amounts of H2S were 0.94 and 4.18 wt%

in the gaseous products for pyrolysis of TT and PCT,

respectively. The other sulphur gaseous products were also

determined by GC–SCD. However, the quantification of

each gaseous product could not be managed since each

component was in trace amount.

The COx gases from pyrolysis of scrap tires have also

been found by other researchers [1,8,11,13]. The COx gases

must be derived from oxygenated compounds such as

stearic acid, extender oils which is used in tire manufacture.

Table 4 shows that methane and hydrogen are the most

predominant products. Cypres et al. suggested that hydrogen

and methane were derived from secondary aromatization

reactions [14]. Similarly, Williams and Taylor have shown

that hydrogen, methane and ethene resulted from secondary

aromatization reactions which produce aromatic hydrocar-

bons [15]. It has also been shown that in some cases

molecular hydrogen may be formed as a primary stable

product from branched alkenes [16]. It is suggested that C4

(butenes and butanes) are formed from the degradation of

polymer–styrene–butadiene rubber (SBR) [1,3]. In this

study, C4 might be generated both from SBR and BR. C2

and C3 were generated both directly from the degradation of

the polymer and by secondary reactions among the primary

degradation products [8].

The contents of hydrocarbon gaseous products were

similar in both PCT and TT derived gas products. However,

PCT-pyrolysis gases contained lower amount of CO2 and

but higher amount of H2S than that of TT-pyrolysis gases. It

is known that H2S comes from the sulphur links in the

vulcanized rubber structure. Although, the sulphur contents

of scrap tires (Table 2) were similar, H2S contents in

pyrolysis gases were significantly different from each other.

This will be discussed later in the text. Moreover, pyrolysis

gases had high gross calorific values about 60–65 MJ NmK3

and that are sufficient to provide the energy requirements of

the pyrolysis plant.

3.3. Composition of pyrolytic oils

The pyrolytic oils obtained from pyrolysis of scrap

passenger car tire and truck tire were characterized in terms

of both fuel characteristics and chemical composition. Some

properties of pyrolytic oils are shown in Table 5. Pyrolytic

oils from pyrolysis of PCT and TT were denoted as PCTO

and TTO, respectively. For comparison purpose, the

chemical and physical properties of commercial diesel are

also presented in Table 5. Specific gravity of pyrolytic oils

was found higher than that of the commercial diesel fuel.

Table 5

Some properties of pyrolytic oils from pyrolysis of scrap tires at 650 8C

PCTO TTO Commercial diesel

Specific gravity, g cmK3 0.9430 0.9130 0.82–0.86

Viscosity at 40 8C, cSt 4.6224 3.8530 2.0–4.5

Flash point, 8C !30 !30 O55

GCVa, MJ kgK1 41.6 42.4 45.1

Elemental analysis, wt%

C 87.57 86.47 86.50

H 10.35 11.73 13.20

N !1 !1 !1

S 1.35 0.83 !0.70

a Gross calorific value.

Table 7

Major compounds detected in pyrolytic liquid from pyrolysis of PCT at

650 8C

tR (min) Compound Area (%)

0.801 2-Methyl-1,3-butadiene 1.12

1.060 Benzene 1.10

1.595 Toluene 10.55

2.720 Ethylbenzene 12.16

2.847 p-Xylene 1.36

3.221 Styrene 8.94

4.144 Isopropylbenzene 2.39

5.116 Propylbenzene 2.07

5.631 4-Methylpyridine 1.34

6.668 a-Methylstyrene 1.76

7.866 1-Methyl-2-isopropylbenzene 1.55

22.900 2,4 0-Dimethyl-1,1 0-biphenyl 2.50

24.194 1,1 0-(1,3-Propanediyl)bis-benzene 2.53

27.002 1-(1-Cyclopenten-1,1-cyclopenten-1-

yl)naphthalene

1.12

33.392 Terphenyl 2.28

Table 8

Major compounds detected in pyrolytic liquid from pyrolysis of TT at

650 8C

tR (min) Compound Area (%)

0.815 1,4-Pentadiene 4.69

1.060 Benzene 2.29

S. Ucar et al. / Fuel 84 (2005) 1884–18921888

The viscosity of oils from both TT and PCT lies in the range

of diesel fuels. As expected, flash points of oils are

comparatively lower than that of diesel fuels. These results

are in good agreement with the previous reports [3,4].

The calorific values for pyrolytic oils were close to that of

commercial diesel. Therefore, the pyrolytic oils can be used

as fuels for combustion systems in industry. Elemental

composition of pyrolytic oils from TT and PCT was found

similar with commercial diesel. However, the sulphur

content in PCTO and TTO was found higher than that of

commercial diesel. It is noted that the sulphur content in the

TTO was less than that of PCTO. In this study, hydrocarbon

types of the pyrolytic oils were determined by using 1H NMR

analysis [17]. The hydrocarbon types in the pyrolytic oils

depending on the pyrolysis temperature are shown in Table 6.

The pyrolytic oils from PCT pyrolysis contain more amounts

of aromatics than the pyrolytic oils from TT pyrolysis. The

aromatic content of pyrolytic oils is due on the one hand to the

aromatic nature of the source rubber material and on the other

hand to cyclization of olefin structures followed by

dehydrogenation reactions and the Diels Alder reactions. In

the present study, it may be considered that formation of

aromatic hydrocarbons from alkenes via the Diels–Alder

reactions dominantly occurred during pyrolysis of PCT,

which contains mostly Butadiene Rubber (BR) [3].

Tables 7 and 8 show major compounds detected by GC-

MS in pyrolytic oils from pyrolysis of PCT and TT. PCTO

contained mainly ethyl benzene, toluene, styrene and with

formation of other hydrocarbons, i.e. propyl benzene,

isopropyl benzene, a-methyl styrene, polycyclic aromatic

hydrocarbons (PAH). However, major compound was found

limonene and with formation other hydrocarbons, i.e.

Table 6

The effect of temperature on the hydrocarbon types in the pyrolytic oils,

vol%

Type of pyrolytic

oil

PCTO TTO

Temperature, 8C 550 650 800 550 650 800

Aromatics 41.54 41.21 41.15 15.41 15.29 15.22

Paraffins 54.55 54.85 54.88 64.12 64.31 64.45

Olefins 3.91 3.94 3.97 20.47 20.40 20.33

toluene, ethyl benzene, p-xylene, 1,4-pentadiene, PAH for

TTO. It is known that limonene is the most important product

from pyrolysis of polyisoprene (NR) [2]. For PCTO and

TTO, some aromatic hydrocarbons containing sulphur,

nitrogen and oxygen were also determined as minor

hydrocarbons. However, the relative amount of these

compounds was quite low.

According to the results of 1H NMR (Table 6), the

aromatic content of PCTO was found higher than that of

TTO. These results are also supported by the GC–MS results.

The difference in the aromatic content of pyrolytic oils may

stem from two possible reasons. One is the difference in the

composition of raw material, the NR content in PCT was

35 wt% and it was 51 wt% in the TT. Another one is that

limonene and/or limonene precursors might have reacted

with pyrolysis products of BR components.

The boiling point distributions of hydrocarbons in

pyrolytic oils from pyrolysis of TT and PCT at the

temperatures of 550, 650 and 800 8C are shown in Fig. 2 as

simulated distillation curves. For comparison purpose,

1.457 3-Methyl-(Z)-1,3,5-hexatriene 1.39

1.597 Toluene 7.53

2.726 Ethylbenzene 2.70

2.892 p-Xylene 4.30

5.207 Propylbenzene 4.73

6.644 a-Methylstyrene 1.84

7.836 1-Methyl-2-isopropylbenzene 2.95

8.121 Limonene 28.78

21.548 2,3,6-Trimethylnaphthalene 2.15

29.615 n-Hexadecanitrile 2.45

33.397 Terphenyl 3.46

0

50

100

150

200

250

300

350

400

450

Boi

ling

Poi

nt, ˚

C

0

50

100

150

200

250

300

350

400

450

Boi

ling

Poi

nt, ˚

C

0

50

100

150

200

250

300

350

400

450

Boi

ling

Poi

nt, ˚

C

PCT

TT

Diesel FuelCommercial Gasoline

PCTTTDiesel FuelCommercial Gasoline

0 10 20 30 40 50 60 70 80 90 100

Cumulative Volume, %

0 10 20 30 40 50 60 70 80 90 100

Cumulative Volume, %

0 10 20 30 40 50 60 70 80 90 100

Cumulative Volume, %

PCTTTDiesel FuelCommercial Gasoline

(a)

(b)

(c)

Fig. 2. Simulated distillation curves of pyrolytic oils from pyrolysis of scrap tires, commercial naphtha and diesel. (a) 550 8C, (b) 650 8C, (c) 800 8C.

S. Ucar et al. / Fuel 84 (2005) 1884–1892 1889

the simulated distillation curves of commercial gasoline and

diesel fuel are also presented in Fig. 2. It can be clearly seen

from Fig. 2 that there is no significant change in the boiling

point distributions of hydrocarbons in pyrolytic oils with

increasing the temperature. The pyrolytic oils from both TT

and PCT have a wide boiling point range. At 550 8C, PCTO

contained about 50% gasoline fraction (boiling point range

!172 8C), whereas gasoline fraction in TTO was 40%. By

increasing the temperatures from 550 to 800 8C, gasoline

fraction did not change significantly. It should be noted that

the initial boiling points of pyrolytic oils (65–72 and

57–60 8C for PCTO and TTO, respectively) were lower

than that of diesel fuel but higher than that of commercial

gasoline. Similar results have also been reported by Day et al.

[18]. It can be concluded that the pyrolytic oils from pyrolysis

of PCT and TT can be blended with the gasoline or diesel

fuels after treatments such as desulphurization and

hydrogenation.

3.4. Production of from CBp from the pyrolysis of scrap tires

3.4.1. Demineralization of CBp

One of the aims of this study was to produce activated

carbon from solid residue of scrap tire pyrolysis. Table 9

shows the some physical properties of the pyrolytic carbon

blacks (CBp) from pyrolysis of scrap tires depending on

the pyrolysis temperature. Fixed carbon contents in

pyrolytic carbon blacks did not change with the pyrolysis

Table 9

Some physico-chemical properties of the pyrolytic carbon blacks (CBp) (mean valueGstandard deviation)

Pyrolysis temperature, 8C PCT derived CBp TT derived CBp

550 650 800 550 650 800

Ash, wt% 40.3G1.2 40.8G1.3 40.8G1.2 14.3G1.5 14.8G1.3 13.5G1.4

Fixed carbon, wt% 56.3G1.9 56.2G2.1 55.9G1.9 82.4G2.5 82.6G2.2 84.3G2.3

GCVa, MJ kgK1 14.8G0.4 15.7G0.3 15.2G0.4 33.9G0.4 33.4G0.3 34.2G0.5

S, wt% 0.8G0.02 1.0G0.04 0.9G0.02 2.1G0.03 2.3G0.03 2.0G0.02

BET surface area, m2 gK1 55.5G4 60.5G5 63.5G5 56.5G5 63.5G4 66.0G6

a Gross calorific value.

S. Ucar et al. / Fuel 84 (2005) 1884–18921890

temperature. Because of the high ash content in PCT, PCT

derived CBp contained higher amount of ash content than

that of TT derived CBp. A wide range of ash contents of

CBp’s has been reported in the literature. For instance,

Wolfson et al. [19] reported a wide range of ash contents

from 7.0 to 16.5 wt%, Darmstadt et al. [20] 14.7 wt% and

Merchant and Petrich [21] 11.1 wt%. The ash content of

PCT derived CBp was found higher than that of previous

works but the ash content of TT derived CBp was found

similar to the literature reported. Because of the low ash

content, the gross calorific value of TT derived CBp was

higher than that of PCT. The fact that the TT derived CBp

contained more sulphur than that of PCT is due to the

binding of the sulphur with the inorganics in TT during

pyrolysis as mentioned before.

Pyrolytic carbons obtained at 800 8C were deminera-

lized. By demineralization, the ash content of TT derived

CBp was decreased from 14–15 to 4–5 wt%. However, the

ash content of PCT derived CBp was decreased from 40 to

38 wt%. The reason is that PCT derived CBp contained

higher Si (38.0 wt%) than that of TT derived CBp

(5.1 wt%). Because of the low ash content, TT derived

CBp was selected for the further applications.

The effect of pyrolysis temperature and demineralization

of CBp on BET surface area is shown in Table 10. BET

surface areas of non-demineralized CBp and demineralized

CBp was not significantly changed with increasing of

pyrolysis temperature. In addition, acid demineralization

had no considerable effect on the surface area as well. Similar

results have been also reported by Cunliffe et al. [22]. They

carried out the pyrolysis of scrap tires at 450–600 8C. The

surface area of the CBp was 61–65 m2 gK1 and increased to

63–74 m2 gK1 with the treatment of acid demineralization.

SEM images of pyrolytic carbon black and demineralized

pyrolytic carbon black are shown in Fig. 3. Before

demineralization process, metals on the surface of CBp

Table 10

BET surface areas of TT derived CBp’s

Pyrolytic carbon

black

Non-demineralized CBp Demineralized CBp

Pyrolysis

temperature, 8C

550 650 800 550 650 800

BET surface

area, m2 gK1

56.5 63.5 66.0 64.2 70.8 72.2

were clearly seen in SEM images. However, after deminer-

alization, SEM images showed that the inorganic com-

ponents on the surface of CBp were partially removed.

3.4.2. Activation of CBp

Demineralized and non-demineralized TT derived CBp

were activated with CO2 (flow rate: 350 ml/min) at 900 8C

for 2, 4, 6 and 8 h, respectively. Fig. 4 shows the influence of

activation time on the degree of burnoff in CO2 achieved for

both demineralized and non-demineralized TT derived

CBp’s. The carbon burnoff exhibited a linear increase

with increasing activation time for both demineralized and

non-demineralized of CBp’s. San Miguel et al. [23] studied

the characteristics of activated carbons produced by

steam and carbon dioxide activation of scrap tires rubber.

They reported that activation of the chars at higher

Fig. 3. SEM images of TT derived CBp’s. (a) Before demineralization,

(b) after demineralization.

Fig. 5. SEM images of TT derived CBp’s. (a) Demineralized CBp, (b)

activated-demineralized CBp.

0

5

10

15

20

25

0 120 240 360 480Actvation time, min.

Bur

n-of

f, w

t %

non-demineralized CBpdemineralized CBp

Fig. 4. Carbon burnoff in CO2 for the demineralized and non-demineralized

TT derived CBp’s in relation to activation time.

S. Ucar et al. / Fuel 84 (2005) 1884–1892 1891

temperatures (950–1100 8C) resulted in a progressive

increase of the value of carbon burnoff, which followed a

linear relationship with the activation time. As can be seen

from Fig. 4, the non-demineralized CBp was more reactive

than demineralized CBp. It is clear that acid treatment

decreased the reactivity of CBp since CBp reactivity is

related to the ash content of the carbonaceous materials [24].

Several other researchers have also mentioned that some

inorganic compounds showed catalytic effect on gasification

[22,25,26]. A key property of activated carbons is their

surface area. Commercial activated carbons typically have a

surface area in the range from 400 to 1500 m2 gK1 [27,28].

The effect of activation time on the BET surface areas of

CBp’s are presented in Table 11. The BET surface area of

CBp was considerably increased by the increasing the

activation time up to 6 h, but further increased in activation

time did not considerably influence the surface area of CBp’s.

The surface areas of activated CBp’s are lower than that of

reported in the literature [29,30] and commercial activated

carbon. The reason may be due to the activation conditions

(temperature, CO2 flow rate etc.) and/or CBp sample.

SEM images of demineralized CBp and activated-

demineralized CBp are shown in Fig. 5. It is clear that the

homogeneous distribution of particles was observed on the

surface by activation of demineralized CBp (Fig. 5).

3.5. Distribution of sulphur in pyrolysis products

It is known that some of sulphur present in tyre are

transferred into gas or liquid products as H2S and

S-compounds where as some part remains in carbon

black. There is a specific interest in the fate of sulphur

compounds due to environmental concerns. Rodriquez

reported that more than 50% of the tyre sulphur was left

Table 11

The effect of activation time on BET surface areas (m2/g) of TT derived

CBp’s

Activation time, h 0 2 4 6 8

Non-demineralized CBp 66.0 91.0 160.7 235.5 240.1

Demineralized CBp 72.2 110.7 164.1 199.6 204.5

in the carbon black [1]. In contrast, Napoli et al. found that

only approximately 25 wt% of tyre sulphur was present in

the carbon black [31]. Tang et al. studied the rubber

pyrolysis in thermal plasma reactor to investigate the

influence of feed rate, steam injection and dolomite addition

on sulphur distribution and transformation [32]. Increasing

feed rate, addition of steam or dolomite increased the share

of total sulphur in carbon black. The content of sulphur in

carbon black could reach more than 80% of total sulphur in

tyre. Inorganic sulphides such as FeS2 and ZnS as well as

element sulphur have been identified in the carbon black. It

has been reported that the ZnO and sulphur is present in tyre

react during pyrolysis to form ZnS [20,33].

By comparing the distribution of total sulphur in the

pyrolysis products (Table 12), it is seen that in the case of

TT, the sulphur is mainly distributed in solid residue,

whereas it is distributed in gas and liquid products in the

pyrolysis of PCT. The reason might stem from the

difference in the ash components between TT and PCT.

Table 12

The distribution of sulphur in pyrolysis products, % (calculated from

sulphur mass balance)

Gas Liquid Solid

PCT 39.2 37.4 23.4

TT 16.6 31.3 52.1

S. Ucar et al. / Fuel 84 (2005) 1884–18921892

High amount of sulphur in solid residue shows that

inorganic components in TT bind the sulphur formed during

pyrolysis. In the residue (CBp), sulphur probably is

chemically bonded mainly in the form of non-volatile

inorganic sulphides and elemental sulphur as well as trace

organic sulphides as suggested by other researchers [22].

4. Conclusions

Two types of scrap tire have been pyrolyzed at the

temperatures of 550, 650 and 800 8C under nitrogen

atmosphere. The effect of the differences in the polymer

types of scrap tires on the pyrolysis yields (gas, oil and

carbon black) and oil composition was studied. The main

conclusions are as follows;

†

There is no any remarkable effect of the pyrolysis tempera-

ture on the product distribution for both TT and PCT.

†

Pyrolysis of TT gave the more amount of oil and less

amount of carbon black than that of PCT.

†

Although the amounts of the hydrocarbon gases from

pyrolysis of PCT and TT were similar, the amounts of

H2S and CO2 from the pyrolysis of PCT were higher than

that of pyrolysis of TT due to the difference in the type of

additives used in tire manufacture.

†

Physical properties of oils from pyrolysis of PCT and TT

were found similar. However, aromatic content and sulphur

content of oil from PCT was higher than that of TT.

†

The pyrolytic oil from pyrolysis of PCT contained about

50% gasoline fraction whereas gasoline fraction in

pyrolytic oil from pyrolysis of TT was 40%. The pyrolytic

oil from pyrolysis of TT can be blended with the gasoline or

diesel fuels after the upgrading such as desulphurization

and hydrogenation. On the other hand, the pyrolytic oil

from PCT can be considered as feedstock for the production

of basic aromatics in petrochemical industry.

†

The utilization of pyrolytic carbon blacks in the

production of activated carbon depends on the type of

inorganic additives in tire manufacture instead of the

polymer types in the scrap tires. The TT derived

pyrolytic carbon black was found more suitable than

from PCT derived CBp for the production of activated

carbon due to its low ash content.

Consequently, evaluation of scrap tires by pyrolysis is

very important from economic and environmental view-

point as all pyrolysis products (gas, liquid and carbon black)

can be utilized. However, further studies are necessary to

utilize pyrolytic oils as a liquid fuel or feedstock.

Acknowledgements

This work was supported by Ege University, Faculty of

Science, under the contracts 2001/Fen/060 and 03/Bil/007.

We would like to thank to the scientific and technical

council of Turkey (TUBITAK) for financial support under

the contract TBAG-AY/279 (102T133). It is a pleasure to

thank Mr Burhan Balikci from Brisa Co, Izmit, Turkey for

analysis support. Many special thanks go to Mr Musa

Karaduman for technical assistance in the laboratory.

References

[1] Rodriguez IM, Laresgoiti MF, Cabrero MA, Torres A, Chomon MJ,

Caballero BM. Fuel Process Tech 2001;72:9–22 [and references

therein].

[2] Mastral AM, Murillo R, Callen MS, Garcia T, Snape CE. Energy

Fuels 2000;14:739–44.

[3] Cunliffe AM, Williams PT. J Anal Appl Pyrolysis 1998;44:131–52.

[4] Roy C, Chaala A, Darmstadt H. J Anal Appl Pyrolysis 1999;51:

201–21.

[5] Williams PT, Brindle AJ. Fuel 2003;82:1023–31.

[6] ASTM D2887-89. Test method for boiling range distribution of

petroleum fractions by gas chromatography, vol. 05.02; 1989.

[7] Laresgoiti MF, Caballero BM, De Marco I, Torres A, Cabrero MA,

Chomon MJ. J Anal Appl Pyrolysis 2004;71:917–34.

[8] Laresgoiti MF, De Marco I, Torres A, Caballero B, Cabrero MA,

Chomon MJ. J Anal Appl Pyrolysis 2000;55:43–54.

[9] Day M, Shen Z, Cooney JD. J Anal Appl Pyrolysis 1999;51:181–200.

[10] Dai X, Yin X, Wu C, Zhang W, Chen Y. Energy 2001;26:385–99.

[11] Gonzalez JF, Encinar JM, Canito JL, Rodriguez JJ. J Anal Appl

Pyrolysis 2001;58–59:667–83.

[12] Williams PT, Besle S, Taylor DT. Fuel 1990;69(12):1474–82.

[13] Williams PT, Brindle AJ. J Anal Appl Pyrolysis 2003;67:143–64.

[14] Cypres R, Bettens B. In: Ferrero GL, Mariatis K, Buckens A,

Bridgewater AV, editors. Pyrolysis and gasification. Barking, UK:

Elsevier Applied Science; 1989.

[15] Williams PT, Taylor DT. Fuel 1993;72:1469–74.

[16] Abbot J, Wojciechowski BW. J Catal 1988;113:353–66.

[17] Myers ME, Stollsteimer JR, Wims AM. Anal Chem 1975;47(12):

2010–5.

[18] Day M, Cooney JD, Shen Z. J Anal Appl Pyrolysis 1996;37:49–67.

[19] Wolfson DE, Beckman JA, Walters JG. US Department of the Interior

Bureau of Mines Report of Investigations; 1969, 7302.

[20] Darmstadt H, Roy C, Kaliguine S. Carbon 1995;33:1449–55.

[21] Merchant AA, Petrich MA. Am I Chem Eng J 1993;39:1370–6.

[22] Cunliffe AM, Williams PT. Energy Fuels 1999;13:166–75.

[23] San Miguel G, Fowler GD, Sollars CJ. Carbon 2003;41:1009–16.

[24] Iniesta E, Sanchez F, Garcia AN, Marcilla A. J Anal Appl Pyrolysis

2001;58–59:983–94.

[25] Samaras P, Diamadopoulos E, Sakellaropoulos GP. Fuel 1996;75:

1108–14.

[26] Cazorla-Amoros D, Ribes-Perez D, Roman-Martinez MC, Linares-

Solano A. Carbon 1996;34:869–78.

[27] Williams PT. Waste treatment and disposal. Chichester: Wiley; 1998.

[28] Bansal RC, Donnet JB, Stoeckli F. Active carbon. New York and

Basel: Marcel and Dekker Inc; 1988.

[29] Helleur R, Popovic N, Ikura M, Stanciulescu M, Liu D. J Anal Appl

Pyrolysis 2001;58-59:813–24.

[30] Lehmann CMB, Rostam-Abadi M, Road MJ, Sun J. Energy Fuels

1998;12:1095–9.

[31] Napoli A, Soudais Y, Lecomte D, Castillo S. J Anal Appl Pyrolysis

1997;40-41:373–82.

[32] Tang L, Huang H. J Anal Appl Pyrolysis 2004;72:35–40.

[33] Mastral AM, Alvarez R, Callen MS, Clemente C, Murillo R. Ind Eng

Chem Res 1999;38:2856–60.